The present invention relates to an apparatus and a method for realizing an all-optical NOR logic device using the gain saturation characteristics of a semiconductor optical amplifier SOA. More particularly, the invention relates to a 10 Gbit/s all-optical NOR logic device among all-optical logic devices, in which a signal transmitted from a given point of an optical circuit such as an optical computing circuit is used as a pump signal and a probe signal.
The recent trends show that the requirement for a high capacity and a high speed system is exponentially increasing.
Most of the present systems are based on silicon materials which operate on the basis of electric signals. For this reason, their future reliability is somewhat uncertain since they are expected to face a serious limitation in terms of their speed and the quantity of information that can be processed.
On the contrary, the systems utilizing the optical devices which are based on Indium Phosphide (InP) are expected to easily overcome all aspects of the aforementioned problems including the speed and quantity of information that can be processed by the systems.
When a system is being configured in general, the method which is based on integrating the single logic devices (AND, OR, XOR, NAND, NOR, NXOR) is utilized. This is also true in case of configuring an optical system.
The logic devices which have two stable states known as logic 0 and 1 are the basic building blocks of a digital computer.
Computers codify all the information using the two logic states. Accordingly, it is certain that logic devices will play a significant role in the development of all-optical logic devices and optoelectronic devices for the future information technology.
Up to the present, all-optical logic devices for ultra-high speed optical information processing utilize either the nonlinear characteristics or wavelength conversion characteristics of light.
Especially, implementations of all-optical NOR logic devices using the nonlinear gain of the SOA are listed chronologically as below;    (1) NOR based on a single-arm ultra-fast nonlinear interferometer (N. S. Patel, et al., Opt. Lett., 21, 1446 (1996))    (2) All-optical NOR implemented by two pump signals with the same wavelength (A. Sharaiha, H. W. L I, F. Matchese and J. Le Bihan, Electron. Lett., 33, 323(1997))    (3) All-optical NOR implemented by two pump signals with two different wavelengths (Young Tae Byun, Sang Hyuck Kim, Deok Ha Woo, Seok Lee, Dong Hwan Kim and Sun Ho Kim, New Physics, 40, 560(2000)), Apparatus and method for realizing All-optical NOR logic device (Young Tae Byun, Sang Hyuck Kim, Deok Ha Woo, Seok Lee, Dong Hwan Kim and Sun Ho Kim, U.S. Pat. No. 6,424,438 B1, Date of patent: Jul. 23, 2002)    (4) All-optical NOR implemented by connecting two semiconductor optical amplifiers (Ali Hamie, Ammar Sharaiha, Mikael Guegan and Benoit Pucel, IEEE Photon. Technol. Lett., 14, 1439 (2002)).
All-optical NOR logic devices that utilizes an ultra-fast nonlinear interferometer (UNI) as shown in (1) has an advantage of being able to operate at high speed.
However, it is unsuitable for an application in optical operating systems which require a high degree of integration. Also, their essential components consist of complicated optical fiber devices whose integration with other devices are also difficult.
On the contrary, all-optical logic devices which utilize the SOA are stable and small in size. They also have the advantages of being easily integrated with other optical devices and are independent of polarization and wavelength (T. Fjeld, D. Wolfson, A. kloch, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt and M. Renaud, Electron. Lett., 36, 1863(2000)).
However, if only the nonlinear characteristic of single SOA is utilized without the optical fiber interferometer, then the structure of an all-optical logic NOR becomes simple and the integration with other devices is possible. However, its operating speed is less than 100 MHz.
In addition, an all-optical NOR logic device implemented by connecting two SOAs as listed in (4) has a better on/off ratio in a wide wavelength region in comparison to an all-optical NOR logic device that utilizes single SOA. However, its operating speed becomes below 62.5 MHz.
More specifically, in the conventional all-optical NOR logic devices as listed in (2) to (4), which do not use the optical fiber interferometer, a pump signal is None-Return to Zero (NRZ) pattern by using a square wave. In addition, a laser beam of continuous wave (CW) light is utilized as a probe signal.
In this case, the operating speed of the all-optical NOR logic devices is constrained to below 100 MHz due to the NRZ pattern of the pump signal and the CW light of the probe signal.
Accordingly, it is imperative to develop an all-optical NOR logic device which is not only possible to be integrated with other optical devices but also has a simple structure and an improved operating speed more than 10 GHz.